The overall goal of this project is to develop an improved dental composite with low polymerization stress using nanoclay fillers producing improved mechanical properties combined with BisGMA/TEGDEMA and/or oxirane resins. This project is an interdisciplinary effort involving three separate institutions, UMKC, UMR, and Mo-Sci Company. Hypothesis 1 (nanoclay fillers) The addition of nanoclay fillers will improve the mechanical properties of the BisGMA/TEGDMA (50:50) and UVR6105/GY281/PTHF (48:48:4) resin systems. Specific Aim: To determine an optimum surface modification and concentration of nanoclay fillers in each polymer matrix system, (see hypothesis 2 below), in order to select a binder-nanoparticle system that will provide optimal mechanical properties in a hybrid filled composite (see hypothesis 3 below). Hypothesis 2 (stress-reducing polymer) The incorporation of a spiroorthocarbonate (TOSU) into two different matrix resins, Bisphenol-A-glycidyldimethacrylate (BisGMA)/ triethylene glycol dimethacrylate (TEGDMA) (50:50) and 3,4-epoxycyclohexylmethyl-3,4-epoxycyclo-hexylcarboxylate (UVR6105)/Diglycidyl ether of Bisphenol F (GY281)/Poly(tetrahydrofuran) (PTHF) (48:48:4), will reduce the polymerization stress of the neat resins. Specific Aim 1 To determine the most appropriate spiroorthocarbonate and the optimal addition level that will significantly reduce the polymerization stress of BisGMA/TEGDMA. The TOSUs will be added to the resin at weight percents of 0, 1, 5, 10, and 20%. Specific Aim 2 To add two appropriate TOSUs to the UVR6105/GY281/PTHF (48:48:4) resin. The TOSUs will be added in concentrations as specified in Specific Aim 1. Hypothesis 3 (glass fillers) The addition of radio-opaque REAS glass fillers to the matrix resins, will produce a nano-hybrid composite with superior mechanical properties to current dental composites. Specific Aim 1 Select an appropriate alkali-free rare-earth aluminosilicate (REAS) glass that matches the refractive index of the cured resins. This glass will be processed into glass powder of appropriate particle size distribution (PSD) having average diameter between 0.05 and 5 microns. Specific Aim 2 Surface-treat the glass fillers with an appropriate coupling agent (either silane, or titanate or zirconate) will be incorporated into the matrix resin. Criteria for incorporation will include the surface treatment, PSD of the glass particles, and loading level of the glass particles into the composite. Specific aim 3 Compare properties (mechanical, optical, chemical) of alkali-free rare-earth REAS glass-modified composites to commercial dental composites. Successful completion of the proposed research will result in significant contributions to dental public health, including: (a) a restorative with significantly reduced polymerization stress which should increase the durability and longevity of the restoration;(b) a restorative with enhanced depth of cure that can be bulk placed which will save clinical time and resources;and (c) a significantly improved understanding of methacrylate and oxirane-based polymeric materials containing nano-fillers.